1. Field of the Invention
The present invention relates to stereoscopic prints that involve the use of lenticular lenses and more particularly to dot printing technologies for producing dot image prints that are placed on the back of lenticular lenses and express color tones.
2. Description of Related Art
To make posters or advertisement prints more conspicuous to viewers for the purpose of promoting products or services, stereoscopic prints have heretofore been used, which involve the use of lenticular lenses so that the viewers can stereoscopically perceive symbolic images of the products or services. Such stereoscopic prints are produced by dividing images acquired at different angles into strips and arraying the strips on the back of lenticular lenses such that the strips are positioned along the half-cylindrical shapes of the lenticular lenses (for example, see Patent Documents 1 and 2).
Known dot printing methods for producing images to be placed on the back of lenticular lenses include FM (frequency-modulated) screening and AM (amplitude-modulated) screening (for example, see Patent Document 1). FM screening achieves tone representation by the density of dots of the same size, and AM screening, in contrast, by the size of dots. As shown in FIG. 10, another proposed method employs FM screening to randomly print dots A so that the dots A can be dispersed across image strips (see also Patent Document 2).    Patent Document 1: Japanese Patent Laid-Open No. H09-061950    Patent Document 2: Japanese Patent Laid-Open No. 2007-233105
It is desired to arrange as many image strips as possible for the viewer of a stereoscopic print to perceive a detailed stereoscopic image every time the viewer changes his or her viewing position horizontally. If so desired, it is also desirable to print the image of the stereoscopic print at the highest resolution of a printer or press printer. In the case of such random dot printing as in Patent Document 2, however, there are many dots around which no dot is printed. In such cases, a press printer may be unable to print uniform dots, or ink may not be transferred or adhered onto the paper if dots to be printed are considerably small as in the highest resolution of a press printer.
For example, when FM screening is employed to print dots at a resolution of 2,400 dpi with the use of a press printer, the width of an image strip is approximately 10 μm, and the size of a pixel is approximately 10 μm×10 μm. However, typical press printers involve considerable difficulty in printing dots of a size of 10 μm, and accordingly, ink may not be transferred onto the printing paper. This results in many pixels in which dots cannot be printed when dot printing is performed on sparsely distributed pixels such as the ones shown in FIG. 10. Therefore, common practice is to perform dot printing by doubling the size of a pixel, i.e., from 10 μm×10 μm to approximately 20 μm×20 μm, and by thus reducing the resolution to 1,200 dpi. In that case, the number of image strips arranged for one half-cylindrical lens of a lenticular sheet also needs to be reduced to half.